Yes, ported at 8-9", and not able to get lower with any sort of steady reading. Was able to drop down to 5" but I couldn't get it to stay alive.
This carb is a 7115S code, and was originally on an engine with 100 more cubic inches. It is entirely possible that it's wildly inappropriate for the engine and I may need to start over. I've been told that the jets are the primary difference between the engines, which is why I've been playing with jets and metering rods.
Car was an auto before, I need to dig into the differences between the auto and manual Duraspark II distributor to see how far off that might be shifting things.
What are the ignition specs between auto and manual? Another thing, if the throttle plate screw is holding the throttle open too far at idle you will not have the enrichment from the off idle port directly above the throttle plate. Which just might cause a flat spot on acceleration.
Another thought, have you manually checked the advance mechanism in the distributor? And the vacuum advance can?
Vigo said:For this one, I started from scratch and reset the idle screw, then backed the throttle and choke screws out enough so they weren't touching. Couldn't get below 8-9" of steady vacuum. Advanced past 20 degrees with virtually no change.
I'm reading this as, you can't ever get below 8" vac on a ported vac port? Is that correct?
Yeesh... idle should have zero vacuum on ported vacuum.
Sound to me either the vacuum port is not ported vacuum, or the engine is idling way up the transfer slots and it will never run right...
Vacuum is way low. Try moving the timing while watching vacuum and see if it goes up.
Time to make a smoke machine and smoke the intake mayhaps? Only surefire way I know to check for intake leaks.
My daily has a snotty cam with tight 108° lobe separation - I had to drill out the idle air passages in the Rochester base plate to get it to idle with the plates out of the transfer slots. Mine idles at 8inHg in drive. Do you have a snotty cam here? If not, I second the smoke machine or equivalent, and find out where the extra air is getting in (or all the vacuum is getting out).
I agree that if you have 8" at idle on a ported vacuum port, that it either ISNT a ported vacuum port, or the throttle plate is set high enough to create vacuum there, and if you get the engine idling well at a lower throttle opening that should 'fix' the ported vacuum port.
Pretty common for the throttle plates to not be perfectly aligned in the bore and not letting them close the whole way.
A properly set-up ported vacuum will have zero vacuum at idle. Up to 1" is acceptable, but something ain't right.
The good news is that we've identified the problem. My suggestion is to take the carb off and loosen the screws in the throttle plates and see if they self-center as it closes.
NOHOME said:Vacuum is way low. Try moving the timing while watching vacuum and see if it goes up.
Time to make a smoke machine and smoke the intake mayhaps? Only surefire way I know to check for intake leaks.
Intake is cast into the head, only other opening is EGR port which has my PCV system plumbed into it. Hose is new and fitting is sealed with PTFE based sealant.
In reply to Curtis73 :
I'll do that tonight.
It's also a stock cam
Ok, pulled apart the carb. Loosened the screws on the throttle plate and had the throttle move a very small amount, maybe 3-4°? Tightened it after. Searching for a gasket set now.
Also held it up to the light after I did that. How much light is normal to see around the throttle plate?
Also, for those wondering about the ports, there is one marked EGR and one marked DIS. EGR is capped and DIS is going to the distributor.
I tried to rebuild a YFA once. Wouldn't hold idle, so I bought a new one. I think it was the first carb I ever tried to rebuild.
That was not cheap back then. It is cheap now. I saw brand new ones for well under $100 on eBay. Crazy.
I would double check your base gasket to be sure it fits the manifold and carburetor properly. Some of the "universal" gaskets included in rebuild kits are too universal and the extra ports they put in the gasket sometimes lead outside and create a vacuum leak.
Also, did this base and body originally belong together? Some carbs (Rochester 2GC comes to mind) have different bases and bodies over different models. They will bolt together but the ports won't line up and you'll get leaks.
Mr_Asa said:Ok, pulled apart the carb. Loosened the screws on the throttle plate and had the throttle move a very small amount, maybe 3-4°? Tightened it after. Searching for a gasket set now.
Also held it up to the light after I did that. How much light is normal to see around the throttle plate?
Also, for those wondering about the ports, there is one marked EGR and one marked DIS. EGR is capped and DIS is going to the distributor.
3-4 degrees is huge. That could mean 400 rpms difference.
That much light is a little excess, but acceptable. Strange that it's mostly on the side of the plate. That looks like manufacturing shift. Hard to overcome. Most of the light should come from the tips of the blades and just be a halo. You shouldn't be able to see through it at all, but its normal for some light to bleed around the edges.
In reply to Curtis73 :
I was shifting the plate around in those pics, it probably would have been a halo had I had it lined up properly.
I'll get the gasket kit tomorrow and start over with it. Hopefully this fixes it.
Regarding the EGR and DIS ports. I would have to look it up, but somewhere around 68-69 I think they went from manifold to ported for those dizzys. There were also some that had no connection for ported source. They were mostly older ones or marine versions which don't use vacuum advance. Easy way to tell is to look in the bore just above the upper edge of the throttle plates there will be a pinhole. If it's not there, you can add one. I can walk you through that.
I guess what I'm saying is... just because the hole says DIS doesn't necessarily mean it is ported or manifold. Only easy way is to check with a gauge, and even then it needs to be properly tuned.
It doesn't take much throttle position to get to the point where ported = manifold, so unless it's tuned properly it's hard to tell.
I think you're on the right track. Getting those blades to close further will help a lot.
In reply to ShawnG :
Yeah, I got the gaskets from Mike at https://www.carburetor-parts.com/ one of the places that's highly recommended by the I6 community
Anything is possible, but I see nothing that indicates its the wrong base
I've dealt with him before, his stuff is top-notch. You're probably ok then.
In reply to Mr_Asa :
When you've eliminated all the problems mentioned and are ready to actually tune it don't be afraid to take some very fine grit sandpaper to the metering rod. If it's just off idle then work on making the tip of the rod smaller. On SU needles I tape the top of the needle with masking tape and then Chuck it in a drill spinning at relatively slow speed. I apply the sand paper right where the bog seems to occur.
Look, this is crude. To a generation used to doing key strokes on a computer to tune, impossibly crude. But give it a shot. Finding the right metering rod might not be easy and without a baseline to work on, you're guessing.
But ancient Chinese saying, A marching ant does more damage than a water buffaloes does standing.
translation? Do something and see what happens.
EGR??
In reply to Knurled. :
Maybe Crankcase ventilation?
In reply to Knurled. :
Its a system most people concerned with horsepower get rid of
(I don't know what you're asking here)
Mr_Asa said:In reply to Knurled. :
Its a system most people concerned with horsepower get rid of
(I don't know what you're asking here)
A carb from the 60s should not have an EGR port, given that IIRC it didn't start showing up in cars until 1973.
It doesn't hurt horsepower one bit, the valve shuts at WOT, and it increases engine efficiency at part throttle, but it has vacuum hoses and stuff so bad, I guess.
In reply to Knurled. :
Carb is from a later model F series.
Knurled. said:EGR??
"That's Edgar. He's in the trunk."- Said whenever anybody asked what the illuminated red EGR light meant on the dash of Kevin Emmersons 76 Charger.
Mr_Asa said:In reply to Knurled. :
Its a system most people concerned with horsepower get rid of
(I don't know what you're asking here)
My guess is he was saying it was malfunctioning causing a vacuum leak from the crankcase? You could always shove a plug in the hose and see if the problem changes.
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